Pteranodon

Pteranodon is a genus of pterosaur whose name comes from Ancient Greek words meaning 'wing', 'without', and 'tooth'. It was one of the largest flying reptiles ever known. The biggest kind, P. longiceps, had a wingspan of more than 6 m (20 ft).

Pteranodon lived in the late Cretaceous period. Its fossils have been found in what is now Kansas, Nebraska, Wyoming, South Dakota and Alabama, all in North America. More fossil examples of Pteranodon have been found than of any other pterosaur. Many of them are in good condition, with nearly complete skulls and skeletons. It was an important animal in the sea that covered the middle of North America, known as the Western Interior Seaway.

When the first fossils were found, scientists placed them in groups of toothed pterosaurs, such as Ornithocheirus and Pterodactylus. In 1876, Othniel Charles Marsh said Pteranodon was its own genus. It had no teeth at all, which was unusual for pterosaurs at that time. Over the years, several species were given to Pteranodon, but today only two are recognised: P. longiceps, the type species, and P. sternbergi. A third species, P. maiseyi, may also exist. Some researchers think the last two belong in a separate genus, Geosternbergia, but this is still being discussed. Another genus, Dawndraco, was split off from Pteranodon. It may be the same as Geosternbergia or Pteranodon, depending on whether those genera are valid.

Pteranodon belongs to the family Pteranodontidae, which is part of the clade Pteranodontia. This group also includes nyctosaurids. Together with ornithocheiromorphs, these animals form the larger clade Pteranodontoidea, which is part of the suborder Pterodactyloidea. Pterosaurs such as Pteranodon are not dinosaurs, but they are related to them, as both belong to the clade Avemetatarsalia.

Male and female Pteranodon looked different in size and crest shape. Males had wingspans of 5.6–7.6 m (18–25 ft), while females were smaller, averaging 3.8 m (12 ft). Males also had much larger crests. In P. longiceps, the crests were long and swept backward, while in P. sternbergi, they were tall and upright. Females had wider pelvises than males. Pteranodon is not to be confused with Pterodon (mammal) or Pterodon (plant).

Discovery and history

Pteranodon was the first pterosaur found outside of Europe. Othniel Charles Marsh found its first fossils in 1870 or 1871. They were in the Smoky Hill Chalk of western Kansas, which formed from the Late Cretaceous period. These chalk layers formed at the bottom of the Western Interior Seaway, a large, shallow sea. Marsh's first finds included wing bones and a tooth from an ancient fish, Xiphactinus. He wrongly thought the tooth belonged to the pterosaur. Marsh first named the find Pterodactylus oweni and placed it in the well-known European genus Pterodactylus. Later he renamed his giant North American pterosaur Pterodactylus occidentalis. The earlier name was already used for a European species, Pterodactylus oweni, described by Harry Seeley. Marsh's rival, Edward Drinker Cope, also found specimens of this large pterosaur. He named two species and tried to place them in the European genus Ornithocheirus, but he misspelled the name. Cope's paper was published just five days after Marsh's, which led to a long argument about whose names came first. Later scientists agreed with Marsh.

The first Pteranodon skull was found on May 2, 1876. It was discovered along the Smoky Hill River in Wallace County (now Logan County), Kansas, by Samuel Wendell Williston, a fossil collector who worked for Marsh. These skulls had no teeth but did have bony crests on top. Because of this, Marsh gave the group the name Pteranodon, which means "wing without tooth." Some early names were later moved to other groups. For example, Pteranodon nanus became part of Nyctosaurus. Scientists also talked about an older toothless jaw from the Cambridge Greensand, named Ornithostoma. Some thought this name should replace Pteranodon. However, it was later found to be an improperly named nomen nudum, so Pteranodon kept its name. Newer research suggested it may have been an azhdarchoid, a different kind of toothless pterosaur. Scientists kept reviewing which species were real. In 1966, Harksen named Pteranodon sternbergi for specimens with upright crests. In 1972, Miller created subgenera, including Geosternbergia. Miller also called many older names doubtful. In 1992, S. Christopher Bennett explained that differences between males and females helped account for variation among Pteranodon fossils. By 1994, he had reduced the valid species to two.

Description

Adult male Pteranodon were among the largest pterosaurs. They were the largest flying animals known until the late 20th century, when the giant azhdarchid pterosaurs were discovered. An average adult male had a wingspan of 5.6 m (18 ft). Adult females were much smaller, averaging 3.8 m (12 ft). A large Pteranodon longiceps is estimated to have had a wingspan of 6.25–6.5 m (20.5–21.3 ft). Some even larger ones had wingspans of 7.25–7.6 m (23.8–24.9 ft). Females had short, rounded head crests and wide pelvic canals. Males had narrow hips and very large head crests, which were likely used for display.

Unlike earlier pterosaurs, such as Rhamphorhynchus and Pterodactylus, Pteranodon had toothless beaks, similar to those of birds. The beaks were long and slender, and they ended in thin, sharp points. The most special feature of Pteranodon was its crest on top of its head. It was made of skull bones that stuck up and back. Male Pteranodon sternbergi had a more upright crest. Pteranodon longiceps had a narrower crest that pointed further back. Females of both species had small, rounded crests. The crests were probably mainly used for display. Several of its bones were joined together, which may have added strength during flight.

Paleobiology

Pteranodon's wings were shaped a lot like those of a modern albatross. Its wings had a high aspect ratio of 9:1, compared to 8:1 for the albatross. Most of its flight came from soaring, but it probably needed quick bursts of flapping now and then. A more recent study suggests it used thermals to soar, much like the extinct Pelagornis. It likely took off by leaping into the air with its long front legs. It may also have taken off from water, as has been suggested for Anhanguera.

Main article: Pterosaur § Terrestrial locomotion

For a long time, scientists have argued about whether Pteranodon walked on two legs or four. Trackways suggest it walked on all fours, as a quadrupedal animal. Its diet included fish. Fish bones were found in the stomach area of one specimen, and fish made up most of its diet. Researchers once thought it dipped its beak into the water while flying. It may have dipped while floating on the surface instead. One researcher suggested it could dive by folding back its wings, like the modern gannet.

Pteranodon was known for its skull crest. The crest was probably used mainly for displays during mating, rather than for other jobs. Males and females were different sizes. The crests of males were large and changed as they grew older. Adults came in two size groups, and the larger group was likely male. Females may have outnumbered males two to one. This is why researchers think Pteranodon might have been polygynous, meaning a few males gathered groups of females. Pteranodon grew quickly to adult size and then stopped growing at a set size. This was unlike most reptiles.

Paleoecology

Main articles: Niobrara Formation and Western Interior Seaway

Pteranodon fossils have been found in the Smoky Hill Chalk of the Niobrara Formation. They have also been found in the slightly younger Sharon Springs layers of the Pierre Shale Formation. When Pteranodon lived, a large inland sea called the Western Interior Seaway covered this area. These rock layers have produced famous fossils since 1870. They stretch from Kansas in the United States north to Manitoba in Canada. Pteranodon fossils have only been found in the southern part, in Kansas, Wyoming, and South Dakota. Many fossils have been found in the Canadian part, but no pterosaur fossils have ever been found there. This suggests Pteranodon lived only in the southern part. Some very incomplete pterosaur fossils, possibly Pteranodon, have also been found on the Gulf Coast and the East Coast of the United States. Some bone pieces from the Mooreville Formation of Alabama and the Merchantville Formation of Delaware may have come from Pteranodon. They are too incomplete to be sure.

Pteranodon longiceps shared the sky with Nyctosaurus, a giant-crested pterosaur. Nyctosaurus was rare in this area. The early toothed bird Ichthyornis was also less common. Under the water, the sea was home mainly to invertebrates such as ammonites and squid. Other sea life included sea turtles like Toxochelys, the plesiosaurs Elasmosaurus and Styxosaurus, and the flightless diving bird Parahesperornis. Mosasaurs were the most common large sea reptiles. They included Clidastes, Mosasaurus and Tylosaurus. Some of these sea reptiles are known to have eaten Pteranodon. In 1904, Barnum Brown reported plesiosaur stomach contents with "pterodactyl" bones, most likely from Pteranodon. Land dinosaurs have also been found in the Niobrara Chalk. This suggests that some animals that died on shore were carried out to sea. One hadrosaur appears to have been eaten in part by a shark.

Like some other animals in which males compete to gather groups of females, Pteranodon probably lived mainly on offshore rookeries. There it could nest away from land-based predators and find food far from shore. Most Pteranodon fossils were found in places that were hundreds of kilometres from the coastline at the time.

Classification

Most Pteranodon fossils come from the Niobrara Formation in the central United States. Broadly defined, Pteranodon lived for more than four million years, during the Santonian stage of the Cretaceous period. In 2003, Kenneth Carpenter studied the fossils in this formation. He found that P. sternbergi lived from 88 to 85 million years ago, and P. longiceps lived from 86 to 84.5 million years ago. A possible third species, named Geosternbergia maiseyi by Kellner in 2010, comes from the Sharon Springs member of the Pierre Shale Formation in Kansas, Wyoming, and South Dakota. It lived 81.5 to 80.5 million years ago. Fossils of P. longiceps have been found in rock layers dating to 80 to 78.25 million years ago.

In the early 1990s, Bennett noted that the two main morphs of pteranodont in the Niobrara Formation were separated in time, with little or no overlap. He suggested they were chronospecies in one evolutionary line that lasted about 4 million years, so only one species was present at any time. P. sternbergi was likely the direct ancestor of P. longiceps. Two species are traditionally recognized as valid: Pteranodon longiceps, the type species, and Pteranodon sternbergi. They differ mainly in the shape of the crest on adult males. George F. Sternberg collected P. sternbergi in 1952. Below is a cladogram showing where this genus fits within Pteranodontia.

Researchers have placed these fossils in different ways. In 1972, Halsey Wilkinson Miller argued that the forms were different enough to be placed in separate subgenera. Peter Wellnhofer and others did not adopt these names. In 2010, Alexander Kellner argued that the species belonged in different genera. He placed P. sternbergi and a skull from the Pierre Shale into Geosternbergia. In 2026, new specimens from the Rybushka Formation were studied, and Bogolubovia was identified as a separate species of Pteranodon.

Many other names were given to Pteranodon species over time, but most are now considered to be the same as two or three valid species. Because Pteranodon was known for having no teeth, toothless pterosaur jaws from around the world were often labeled as Pteranodon, which caused confusion. The name became a wastebasket taxon, similar to the dinosaur Megalosaurus. Several subgenera were later proposed, which made the classification even more complicated. Two species, P. oregonensis and P. orientalis, are not pteranodontids. They have been renamed Bennettazhia oregonensis and Bogolubovia orientalis.